1. Field of the Invention
The present invention relates to a device for recording data on and reproducing data from an optical disk in which pre-pits are formed in guiding tracks, the pre-pits including address information. In particular, the present invention relates to a disk device in which an offset included in a tracking error signal is removed, and thereby, an optical beam can be controlled to be incident on a center of an information recording track of the disk accurately.
The present invention may be applied to a disk device for a high-density optical disk such as a DVD-R, an erasable type of the DVD-R, a DVD, or the like.
2. Description of the Related Art
In an optical disk device which can record data on an optical disk, in order to cause a light spot of an optical beam to follow an information recording track formed on the optical disk, a so-called push-pull tracking method is used in which a tracking error signal is obtained from a differential signal of a distribution of diffracted light from the guiding tracks.
In this push-pull tracking method, when an objective lens is moved by tracking control so as to cause the light spot to follow a decentering component of the disk, the diffracted light distribution on a photodetector moves. Due to the movement of the diffracted light distribution, an offset occurs in the tracking error signal.
Further, when the disk is sloped, respective light detection signals of the two divisions of the photodetector, the dividing line of which extends parallel to the tangential line of the information recording track of the disk, are not balanced. Thereby, the tracking error signal is not zero even when the light spot is present at the center of the information recording track. Thereby, track offset occurs.
Thus, it is not possible to position the light spot at the center of the information recording track with high accuracy.
In order to solve such a problem, for example, a pair of optical beams are incident on the optical disk at an interval of an odd-number of times of approximately 1/2 of the track pitch, a pair of beams reflected from the optical disk being incident on a pair of two-division photodetectors, respectively. The tracking error signal is obtained from the difference between the differences in the detection outputs of the respective two-division photodetectors. Such a method is disclosed, for example, as an optical-head tracking-error detecting method in Japanese Patent Publication No.4-34212.
According to this detecting method, it is possible to reduce the track offset.
Further, a method in which, in order to control the position of the optical beam at the center of the information recording track, the tracking error signal including the offset is corrected so that the offset is eliminated. Such a method is disclosed, for example, as an optical tracking method in Japanese Patent Publication No.3-31213.
In this optical tracking method, one or more sets of pre-wobbling tracking pits which are arranged to the right and left of a track are previously provided in a header area of the disk.
Then, when recording data on or reproducing data from the disk, using these pre-wobbling pits, the tracking error signal is obtained in accordance with a pre-wobbling method. The thus-obtained tracking error signal is a correct signal indicating the amount of light spot deviation from the center of the track and does not include the offset. Then, by using the thus-obtained tracking error signal, a push-pull tracking error signal obtained by using the distribution of the light diffracted from a pre-groove having a 1/8 wavelength depth is corrected.
In this optical tracking method, the light spot follows the track with high accuracy and data recording and reproducing can be performed.
An optical system of an optical disk device in the related art will now be described with reference to figures.
FIG. 1 shows a general view of the optical system of the optical disk device. The optical system includes a light source 1 of a laser or the like, a coupling lens 2, a beam splitter 3, a reflecting plate 4, a 1/4-wavelength plate 5, an objective lens 6, a light-converging lens 8, a photodetector 9, and an I/V amplifier 10. The I/V amplifier 10 converts input signals of electric currents into signals of voltages and supplies the output A and the output B.
In the optical disk device shown in FIG. 1, an operation of generating the tracking error signal will now be described simply.
The light emitted from the light source 1 of a laser or the like, is converged on a recording surface 7a of an optical disk 7 through the coupling lens 2, beam splitter 3, reflecting plate 4, 1/4-wavelength plate 5, and objective lens 6.
The light reflected by the recording surface 7a of the optical disk 7 returns to the same optical system, is reflected by the beam splitter 3, and is converged, through the light-converging lens 8, on the photodetector 9. Then, the light signal is converted into an electric signal through the photodetector 9.
Ordinarily, the output of the photodetector 9 is converted into voltages which will undergo various calculations. However, the outputs of the photodetector 9, which comprise electric currents, undergo various calculations as they are.
FIG. 2 is a perspective view showing a structure of the recording surface 7a of the optical disk 7. The recording surface 7a includes information recording tracks 11 (for example, referred to as grooves), the guiding tracks 12 (for example, referred to as lands) and the pre-pits 13.
As shown in FIG. 2, on the recording surface 7a, the information recording track 11 and the guiding track 12 for guiding the optical beam to the information recording track 11 are spirally formed. In the guiding tracks 12, the pre-pits 13 including address information are formed.
A dividing line 9a of the photodetector 9 shown in FIG. 1 is optically approximately parallel to the tangential line of the spiral tracks shown in FIG. 2.
Further, not shown in FIG. 1, a focus servo system for controlling the focal point of the light beam to the recording surface 7a is provided. In some devices, the photodetector 9 is further divided in order to detect the focal point. In the device in which the photodetector 9 is further divided, divisions obtained by the dividing line for dividing the photodetector 9 into the two divisions may be considered as groups, respectively.
As described above as the related art, in order to reduce the offset of the tracking error signal, the optical-head tracking-error detecting method has been proposed in the above-mentioned Japanese Patent Publication No.4-34212.
In this method, a special arrangement using three beams is used. For the detection, it is necessary to divide the light beam into three or more beams. Thereby, when a recording device in which it is difficult to obtain a sufficient intensity of light is used, the light intensity of each division beam may not be sufficient.
Further, in tracking performed on a two-layer optical disk, a pair of the beams adversely affects the main beam.
Further, the optical tracking method in which the tracking error signal including the offset is corrected so that the offset is eliminated has been proposed in Japanese Patent Publication No.8-31213.
In this method, from the pits arranged to the right and left of the track in the header area of the disk, an accurate amount of deviation from the center of the track, which does not include the offset, is detected, and thereby, the push-pull tracking error signal which is obtained by using the light diffracted from the pre-groove is corrected.
In the optical disk on which data can be written, it is necessary to previously record a synchronization signal and address information for searching for a position, as pits, on the optical disk (ordinarily, in the information recording track) at a stage of pre-formatting.
However, the pre-wobbling pits or the address-information pits have no relation to user data. A capacity which can be used for recording user data is reduced as a result of previously recording such pits. Thus, the use efficiency of the disk recording surface is degraded.
When an optical disk (for example, a DVD-R), data of which can be reproduced by a device which is a device only for data reproduction, is produced, it is necessary that data of the optical disk can be reproduced similarly to a case where data of a reproduction-only optical disk (for example, a DVD-ROM) having a special medium format is reproduced.
For this purpose, tracking pre-pits or address-information pits, which are not provided on a reproduction-only optical disk, cannot be formed on the information track of the non-reproduction-only optical disk, data of which can be reproduced by the device which is a device only for data reproduction.
In order to solve such a problem, the optical disk on which address information, which is necessary for the optical disk on which data can be recorded, can be recorded without reduction of recording capacity and without affecting data reproduction through the device for only reproduction has been proposed in Japanese Laid-Open Patent Application No.9-17029, `Optical Disk, Reading Device therefor, and Optical-Disk Manufacturing Method`.
In this optical disk and this reading device therefor, a synchronization signal and address information to be used for a position search are not recorded in the information recording track but are recorded in the guiding tracks as pre-pits. The synchronization signal and address information are read through a system other than the system for processing the reproduction signal.
That is, in this optical disk, the pre-pit information including the address information is recorded in the guiding track which is used for guiding the optical beam.
At this time, the pre-pits are arranged so that the pre-pits are not adjacent to each other. Thus, a medium format of the optical disk medium is special.
In means for detecting the tracking error signal for the optical disk having such a format, the tracking error signal is detected by using a differential signal of signals obtained from two light-receiving elements obtained as a result of a photodetector being divided into the two divisions by the dividing line parallel to or perpendicular to the tracks.